In a modern society, many people always carry devices such as PDAs, mobile phones, medical devices, and the like. Methods of transmitting a signal for communicating data among information terminal devices includes wired transmission methods using cables and wireless transmission methods using waves, light, and the like.
In the wired transmission methods, a security level of transmitted data and a transmission speed of data are high. However, wired devices such as cables have to be always carried. On the other hand, the wireless transmission methods are convenient to transmit data. However, a complex hardware structure is necessary so as to wirelessly transmit data. Accordingly, it is difficult to reduce a price of wireless transmission devices.
Accordingly, a technique of communicating data with a simple hardware structure is necessary.